Re: [PATCH -v4][RFC]: mutex: implement adaptive spinning

[Linus Torvalds]

On Wed, 7 Jan 2009, Chris Mason wrote:
> 
> So far I haven't found any btrfs benchmarks where this is slower than
> mutexes without any spinning.  But, it isn't quite as fast as the btrfs
> spin.

Quite frankly, from our history with ext3 and other filesystems, using a 
mutex in the filesystem is generally the wrong thing to do anyway. 

Are you sure you can't just use a spinlock, and just release it over IO? 
The "have to do IO or extend the btree" case is usually pretty damn clear.

Because it really sounds like you're lock-limited, and you should just try 
to clean it up. A pure "just spinlock" in the hotpath is always going to 
be better.

		Linus
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